High temperature superconducting wires having increased engineering current densities

ABSTRACT

A superconductor wire having a first HTS layer with a first cap layer in direct contact with a first surface of the first HTS layer and a second cap layer in direct contact with a second surface of the first HTS layer. There is a first lamination layer affixed to the first cap layer and a stabilizer layer having a first surface affixed to the second cap layer. There is a second HTS layer and a third cap layer in direct contact with a first surface of the second HTS layer and a fourth cap layer in direct contact with a second surface of the second HTS layer. There is a second lamination layer affixed to the fourth cap layer. The second surface of the stabilizer layer is affixed to the third cap layer and there are first and second fillets disposed along a edge of the laminated superconductor.

FIELD OF INVENTION

The present invention generally relates to long length high temperaturesuperconducting (“HTS”) wires and more particularly to such HTS wireshaving increased engineering current densities.

BACKGROUND

Since the discovery of HTS materials (i.e. material that can retain itssuperconducting properties above the liquid nitrogen temperature of 77K)there have been efforts to develop various engineering applicationsusing such HTS materials. In thin film superconductor devices and wires,most progress has been made with fabrication of devices utilizing anoxide superconductor including yttrium, barium, copper and oxygen in thewell-known basic composition of YBa₂CuO_(7-y), (hereinafter referred toas Y123 or YBCO), which remains the preferred material for manyapplications, including cables, motors, generators, synchronouscondensers, transformers, current limiters, and magnet systems formilitary, high energy physics, materials processing, transportation andmedical uses.

HTS wire based on these YBCO materials, commonly referred to as CoatedConductor or Second Generation (2 G) wire has been manufactured incontinuous lengths of hundreds of meters or longer with critical currentdensities, J_(c), of 3 MA/cm² or higher at 77 K and self-field usingroll-to-roll production lines. The engineering current densities(J_(e)), which take into account the thickness of the substrate and thestabilizer material, of over 8 KA/cm² have been achieved in longlengths.

To continue to make HTS wire more desirable for various powerapplications, increasing the engineering current density is veryimportant. Since the architecture of 2 G wires, having a substrate withone or more buffer layers on which the HTS layer is disposed has beenlong established and required for high performance 2 G wire, focus hasbeen placed on increasing the J_(c) to in turn increase J_(e). As aresult, increases in J_(e) have been somewhat modest as the overallcross-sectional area of the HTS 2 G wire have remained stable due to thethickness of the substrate and stabilizer layers.

In addition, certain substrates used in HTS wires, such as nickeltungsten (Ni5W) have magnetic properties and have resulted in less thanoptimal electrical performance in AC applications. Efforts have focusedon reducing the magnetic properties in such substrates by using lessmagnetic material (e.g. Ni9W), but challenges in maintaining comparableoverall electrical performance characteristics have persisted.

Therefore, there exists a need for an HTS wire with increasedengineering current density as well as an HTS wire with improvedelectrical performance in AC applications.

SUMMARY

It is an object of the invention to produce an HTS wire with increasedengineering current density.

It is a further object of the invention to produce an HTS wire withimproved electrical performance in AC applications.

It is a further object of the invention to produce an HTS wire in whichthe textured substrate is removed in the wire manufacturing process andis reusable to produce another HTS wire with the removed texturedsubstrate.

In one aspect the invention includes a laminated superconductor wireassembly, comprising a first high temperature superconductor layerhaving a first surface and a second surface opposite the first surfaceand a first electrically conductive cap layer overlaying and in directphysical contact with the first surface of the first high temperaturesuperconductor layer. There is a second electrically conductive caplayer overlaying and in direct physical contact with the second surfaceof the first high temperature superconductor layer and a firstlamination layer overlaying and affixed to the first electricallyconductive cap layer. There is also a stabilizer layer, having a firstsurface and a second surface opposite the first surface, the firstsurface of the stabilizer layer overlaying and affixed to the secondelectrically conductive cap layer. There is also a second hightemperature superconductor layer having a first surface and a secondsurface opposite the first surface and a third electrically conductivecap layer overlaying and in direct physical contact with the firstsurface of the second high temperature superconductor layer. There isfurther a fourth electrically conductive cap layer overlaying and indirect physical contact with the second surface of the second hightemperature superconductor layer and a second lamination layeroverlaying and affixed to the fourth electrically conductive cap layer.The second surface of the stabilizer layer is overlaying and affixed tothe third electrically conductive cap layer and there is included afirst fillet disposed along a first edge of the laminated superconductorwire assembly and connected to the first lamination layer and the secondlamination layer. There is a second fillet disposed along a second edgeof the laminated superconductor wire assembly and connected to the firstlamination layer and the second lamination layer.

In other aspects of the invention, one or more of the following featuresmay be included. The first and second high temperature superconductorlayers each may comprise a rare earth-alkaline earth-copper oxide. Thefirst, second, third and fourth electrically conductive cap layers mayeach comprise silver or a silver alloy or a silver layer and copperlayer. The first and second lamination layers may each comprise a metalselected from the group of aluminum, copper, silver, nickel, iron,stainless steel, aluminum alloy, copper alloy, silver alloy, nickelalloy, and iron alloy. The first and second lamination layers may have awidth that is greater than the width of the first and second hightemperature superconductor layers. The width of the first and secondlamination layers may be between 0.01 and 2 mm greater than the width ofthe first and second high temperature superconductor layers. Thestabilizer layer may comprise a metal selected from the group ofaluminum, copper, silver, nickel, iron, stainless steel, aluminum alloy,copper alloy, silver alloy, nickel alloy, and iron alloy. The secondelectrically conductive cap layer may be affixed to the first surface ofthe stabilizer layer via an epoxy or a solder, the fourth electricallyconductive cap layer may be affixed to the second surface of thestabilizer layer via an epoxy or a solder, the first lamination may beaffixed to the first electrically conductive cap layer via an epoxy or asolder, and the second lamination may be affixed to the fourthelectrically conductive cap layer via an epoxy or a solder; and whereinthe first and second fillets may be formed of an epoxy or a solder. Theepoxy may doped with material to make the epoxy electrically conductive,thermally conductive, or electrically and thermally conductive.

In another aspect the invention features a laminated superconductor wireassembly, comprising a high temperature superconductor layer having afirst surface and a second surface opposite the first surface. There isa first electrically conductive cap layer overlaying and in directphysical contact with the first surface of the high temperaturesuperconductor layer. There is also a second electrically conductive caplayer overlaying and in direct physical contact with the second surfaceof the high temperature superconductor layer and a first laminationlayer overlaying and affixed to the first electrically conductive caplayer. There is further included a stabilizer layer, having a firstsurface and a second surface opposite the first surface, the firstsurface of the stabilizer layer overlaying and affixed to the secondelectrically conductive cap layer and a second lamination layeroverlaying and affixed to the second surface of the stabilizer layer.There is included a first fillet disposed along a first edge of thelaminated superconductor wire assembly and connected to the firstlamination layer and the second lamination layer and a second filletdisposed along a second edge of the laminated superconductor wireassembly and connected to the first lamination layer and the secondlamination layer.

In yet other aspects of the invention, one or more of the followingfeatures may be included. The high temperature superconductor layer maycomprise a rare earth-alkaline earth-copper oxide. The first and secondelectrically conductive cap layers may each comprise silver or a silveralloy or a silver layer and a copper layer. The first and secondlamination layers may each comprise a metal selected from the group ofaluminum, copper, silver, nickel, iron, stainless steel, aluminum alloy,copper alloy, silver alloy, nickel alloy, and iron alloy. The first andsecond lamination layers may have a width that is greater than the widthof the first and second high temperature superconductor layers. Thewidth of the first and second lamination layers may be between 0.01 and2 mm greater than the width of the first high temperature superconductorlayer. The stabilizer layer may comprises a metal selected from thegroup of aluminum, copper, silver, nickel, iron, stainless steel,aluminum alloy, copper alloy, silver alloy, nickel alloy, and ironalloy. The second electrically conductive cap layer may be affixed tothe first surface of the stabilizer layer via an epoxy or solder, thefirst lamination may be affixed to the first electrically conductive caplayer via an epoxy or solder and the second lamination may be bonded tothe second with the second surface of the stabilizer layer via an epoxyor solder; and the first and second fillets may be formed of an epoxy ora solder. The epoxy may be doped with material to make the epoxyelectrically conductive, thermally conductive, or electrically andthermally conductive. In one aspect the invention includes a method ofmaking a laminated superconductor wire. The method includes providing afirst superconductor insert having a first high temperaturesuperconductor layer with a first surface overlaying and in directphysical contact with a first biaxially textured substrate and a firstelectrically conductive cap layer overlaying and in direct physicalcontact with a second surface of the first superconductor layer. Themethod also includes providing a second superconductor insert having asecond high temperature superconductor layer with a first surfaceoverlaying and in direct physical contact with a first surface of asecond biaxially textured substrate and a second electrically conductivecap layer overlaying and in direct physical contact with a secondsurface of the second superconductor layer. The method also includesaffixing the first electrically conductive cap layer of the firstsuperconductor insert to a first surface of a stabilizer layer andaffixing the second electrically conductive cap layer of the secondsuperconductor insert to a second surface of a stabilizer layer oppositethe first surface of the stabilizer layer. The method additionallyincludes removing the first biaxially textured substrate from the firstsuperconductor layer to expose the first surface of the firstsuperconductor layer and removing the second biaxially texturedsubstrate from the second superconductor layer to expose the firstsurface of the second superconductor layer. The method further includesaffixing a third electrically conductive cap layer to the first surfaceof the first superconductor layer; and affixing a fourth electricallyconductive cap layer to the first surface of the second superconductorlayer and affixing a first lamination layer to the third electricallyconductive cap layer; and affixing a second lamination layer to thefourth electrically conductive cap layer. The step of affixing the firstand second lamination layers includes disposing a first fillet along afirst edge of the laminated superconductor wire assembly and connectedto the first lamination layer and the second lamination layer anddisposing a second fillet along a second edge of the laminatedsuperconductor wire assembly and connected to the first lamination layerand the second lamination layer.

In other aspects of the invention, one or more of the following featuresmay be included. The first and second high temperature superconductorlayers may each comprise a rare earth-alkaline earth-copper oxide. Thefirst and second biaxially textured substrates may each comprise one ofa hastelloy or a nickel alloy. The first and second biaxially texturedsubstrates may each further comprise at least one buffer layer. Thefirst, second, third and fourth electrically conductive cap layers mayeach comprise silver or a silver alloy or a layer of silver and a layerof copper. The first and second lamination layers may each comprise ametal selected from the group of aluminum, copper, silver, nickel, iron,stainless steel, aluminum alloy, copper alloy, silver alloy, nickelalloy, and iron alloy. The first and second lamination layers may have awidth that is greater than the width of the first and second hightemperature superconductor layers. The width of the first and secondlamination layers may be between 0.01 and 2 mm greater than the width ofthe first and second high temperature superconductor layers. Thestabilizer layer may comprises a metal selected from the group ofaluminum, copper, silver, nickel, iron, stainless steel, aluminum alloy,copper alloy, silver alloy, nickel alloy, and iron alloy. The secondelectrically conductive cap layer may be affixed to the first surface ofthe stabilizer layer via an epoxy or a solder, the fourth electricallyconductive cap layer may be affixed to the second surface of thestabilizer layer via an epoxy or a solder, the first lamination may beaffixed to the first electrically conductive cap layer via an epoxy orsolder, and the second lamination may be affixed to the secondelectrically conductive cap layer via an epoxy or solder; and whereinthe first and second fillets may be formed of an epoxy or a solder. Themethod may also include reusing the first and second biaxially texturedsubstrates removed from the first and second superconductor layers toproduce two superconductor inserts each having a high temperaturesuperconductor layer with a surface overlaying and in direct contactwith one of the removed first and second biaxially textured substrates.

In yet another aspect the invention includes a method of making alaminated superconductor wire, the method comprising providing asuperconductor insert having a high temperature superconductor layerwith a first surface and a second surface opposite the first surface.The first surface overlaying and in direct contact with a biaxiallytextured substrate and a first electrically conductive cap layeroverlaying and in direct physical contact with a second surface of thesuperconductor layer. The method includes affixing the firstelectrically conductive cap layer of the superconductor insert to afirst surface of a stabilizer layer and removing the biaxially texturedsubstrate from the first superconductor layer to expose the firstsurface of the first superconductor layer. The method also includesaffixing a third electrically conductive cap layer to the first surfaceof the superconductor layer, affixing a first lamination layer to thesecond electrically conductive cap layer and affixing a secondlamination layer to a second surface of the stabilizer layer. The stepof affixing the first and second lamination layers includes disposing afirst fillet along a first edge of the laminated superconductor wireassembly and connected to the first lamination layer and the secondlamination layer and disposing a second fillet along a second edge ofthe laminated superconductor wire assembly and connected to the firstlamination layer and the second lamination layer.

In yet further aspects of the invention, one or more of the followingfeatures may be included. The high temperature superconductor layer maycomprise a rare earth-alkaline earth-copper oxide. The biaxiallytextured substrate may comprises one of a hastelloy or a nickel alloy.The biaxially textured substrate may further comprise at least onebuffer layer. The first and second electrically conductive cap layersmay each comprise silver or a silver alloy or a layer of silver and alayer of copper. The first and second lamination layers may eachcomprise a metal selected from the group of aluminum, copper, silver,nickel, iron, stainless steel, aluminum alloy, copper alloy, silveralloy, nickel alloy, and iron alloy. The first and second laminationlayers may have a width that is greater than the width of the hightemperature superconductor layer. The width of the first and secondlamination layers may be between 0.01 and 2 mm greater than the width ofthe high temperature superconductor layer. The stabilizer layer maycomprise a metal selected from the group of aluminum, copper, silver,nickel, iron, stainless steel, aluminum alloy, copper alloy, silveralloy, nickel alloy, and iron alloy. The second electrically conductivecap layer may be affixed to the first surface of the stabilizer layervia an epoxy or solder, the first lamination may be bonded to the firstelectrically conductive cap layer via an epoxy or solder, and the secondlamination may be bonded to the second with the second surface of thestabilizer layer via an epoxy or solder and the first and second filletsmay be formed of an epoxy or a solder. The method may further includereusing the biaxially textured substrate removed from the firstsuperconductor layer to produce a superconductor insert having a hightemperature superconductor layer with a surface overlaying and in directcontact with the removed biaxially textured substrate.

Additional features, advantages, and embodiments of the presentinvention may be set forth from consideration of the following detaileddescription, drawings, and claims. Moreover, it is to be understood thatboth the foregoing summary of the present disclosure and the followingdetailed description are exemplary and intended to provide furtherexplanation without further limiting the scope of the present disclosureclaimed.

DESCRIPTION OF DRAWINGS

FIG. 1 shows the architecture of a prior art 2 G HTS wire.

FIG. 2 illustrates a prior art reel-to-reel process for manufacturingthe 2 G HTS wire of FIG. 1 by the RABiTS/MOD process.

FIG. 3 illustrates a reel to reel process for manufacturing a doublesided HTS wire according to an embodiment of this invention.

FIG. 4 is a cross-sectional view of a double sided HTS wire manufacturedaccording to the reel to reel process of FIG. 3.

FIG. 5 illustrates a reel to reel process for manufacturing a singlesided HTS wire according to another embodiment of this invention.

FIG. 6 is a cross-sectional view of a single sided HTS wire manufacturedaccording to the reel to reel process of FIG. 5.

DETAILED DESCRIPTION

An exemplary architecture of a prior art HTS wire 10 is depicted inFIG. 1. In this architecture, HTS wire 10 includes a polycrystallinesuperconductor layer 12 disposed over and supported by a substrate 16,between which are one or more buffer layers 14. The substrate 16comprises a flexible metal foil which may be formed of any suitablemetal containing material. According to one embodiment, the flexiblemetal substrate is a nickel containing alloy, such as a nickel tungstenalloy.

The substrate 16 may include texture that is transferred to thesuperconductor layer 12. As described herein, texture refers to amicrostructure including crystal plane alignment. A high degree ofcrystal plane alignment in the superconductor layer allows thepolycrystalline superconductor layer 12 to exhibit single crystal-likeperformance. The textured substrate 16 may be a flexible metal film withone of the other layers described above. Alternatively, the texturedsubstrate 16 may be a separate layer within the coated conductor.

The textured substrate 16 may be produced by any appropriate process.According to one embodiment, the textured substrate 16 may be producedby a rolling-assisted biaxially textured substrate (RABiTS) process. TheRABiTS process includes the production of a biaxially textured metalfoil by a rolling assisted process. At least one oxide buffer layer 14is then provided on the textured metal substrate 16, with the oxidebuffer layer exhibiting the same biaxially textured microstructure asthe metal substrate. A biaxially textured high temperaturesuperconductor layer 12 is then deposited over the oxide buffer layer(s)14. The oxide buffer layer 14 prevents the diffusion of metal from thefilm to the superconductor layer.

According to another embodiment, the textured substrate may be producedby a process utilizing ion-beam assisted deposition (IBAD). The IBADprocess includes the ion-beam assisted deposition of a textured ceramicbuffer layer on the surface of an un-textured metal foil. Asuperconductor layer is then deposited over the textured ceramic bufferlayer. Additional buffer layers may be provided between the texturedceramic buffer layer and the superconductor layer and/or between themetal film and the textured ceramic buffer layer. The IBAD coatedconductor includes a metal film substrate, a textured ceramic oxidebuffer layer, oxide buffer layers, a superconductor layer, a metallicprotective layer and a stabilizer layer.

The superconductor layer may be deposited over the substrate of thecoated conductor structure by any suitable process. According to oneembodiment, the superconductor layer may be deposited by a metal-organicdeposition process. According to another embodiment, the superconductorlayer may be deposited by a pulsed laser deposition (PLD), reactiveco-evaporation (RCE), metal-organic chemical vapor deposition (MOCVD),electron beam deposition, chemical vapor deposition (CVD), or sputteringprocess. The superconductor layer may have any appropriate thickness.According to one embodiment, the superconductor layer has a thicknessgreater than 1 μm. In another embodiment, the superconductor layer has athickness in the range of about 1 μm to about 2 μm. According to someembodiments, the superconductor may have a thickness of less than about5 μm.

As is known in the field, HTS wire 10 also may include a metallicprotective layer 18 a, such as an Ag layer, disposed on superconductorlayer 12 and a stabilizer layer 20 a disposed on the metallic layer 18a. HTS wire 10 may also include a metallic protective layer 18 b, suchas an Ag layer, disposed on a surface of substrate 16 opposite thesurface on which the buffer layers 14 are disposed. And, stabilizerlayer 20 b may be disposed on the metallic layer 18 b. The protectivelayer and the stabilizer layer may be referred to herein in combinationas a cap layer.

The protective metal layers (or cap layers) 18 a/18 b are deposited overthe superconductor layer 14 and the substrate 16 for the purpose ofprotecting the superconductor layer/substrate and may be any suitablemetal containing material. According to one embodiment, the protectivemetal layer is a silver layer. The protective layer may have anyappropriate thickness. According to one embodiment, the protective layerhas a thickness of 3 μm. According to another embodiment the protectivelayer has a thickness of about 1 μm. According to another embodiment theprotective layer has a thickness of about 0.5 μm.

According to one embodiment the stabilizer layers 20 a/20 b may includeany suitable metal containing material and may have a thickness greaterthan 25 μm. In another embodiment the stabilizer layers may havethicknesses of 10 to 25 μm. In another embodiment the stabilizer layersmay have thicknesses of about 0.5 μm. In one embodiment the stabilizerlayers are copper. In other embodiments, the stabilizer layers arestainless steel, brass or any other suitable metal containing material.In one embodiment, the width of the stabilizer layers are the same asthat of the HTS layer 12. In another embodiment, the width of thestabilizer layers are greater than that of the HTS layer 12. In anotherembodiment, the stabilizer layer can wrap around all sides of the HTSwire 10.

The superconductor layer 12 may be formed of any appropriatesuperconductor.

According to one embodiment the superconductor layer may be a rare earthmetal-alkaline earth metal-transition metal-oxide superconductor.According to one embodiment, the superconductor layer 12 may contain asuperconductor with the general formula:(RE)Ba₂Cu₃O_(7-δ)

where RE includes at least one rare earth metal and 0≤δ≤0.65. Accordingto another embodiment, the superconductor layer may contain asuperconductor with the general formula:(RE)Ba₂Cu₃O₇

where RE includes at least one rare earth metal. In one embodiment, REmay include yttrium, producing a superconductor layer of the generalformula YBa₂Cu₃O₇ (YBCO). While the superconductor layer will bereferred to herein as a YBCO superconductor layer for the purposes ofconvenience, the methods discussed in this application apply equally toother appropriate superconductor materials. In some cases, RE may be amixture of two or more rare earth metals.

The superconductor layer 12 may also include a dopant in addition to theprimary rare earth metal. The dopant may be a rare earth metal.According to one embodiment, a YBCO superconductor layer may include adysprosium dopant. The dopant may be present in an amount of up to 75%relative to the primary rare earth metal. According to one embodiment,the dopant is present in an amount of at least about 1% and at mostabout 50% of the primary rare earth metal. According to anotherembodiment the dopant may be a transition metal such as Zr, Nb, Ta, Hfor Au. The dopant may combine with other elements in the superconductorto form a single or mixed metal oxide.

In one embodiment, the HTS wire 10 may be sectioned along its length into multiple strips. The sectioning may be done by any appropriate meansincluding laser cutting, roll slitting or punching. Moreover, after theHTS wire 10 is sectioned along its length into multiple strips, thestrips may then be sandwiched between laminations on the outer surfacesof the stabilizer layers 20 a and 20 b, as described below.

By including the laminations as well as the stabilizer layers 20 a and20 b, the HTS wire structure is suitably reinforced mechanically and hasbeen provided with electrical paths from the HTS layer 12 so that it iselectrically stabilized. It is therefore configured to be directlyutilized in an electrical power application such as in a HTS powercable, for example. In certain cases, all that is desired is theso-called “insert” wire which comprises the HTS wire structure of FIG. 1without the laminations layers. As will be described below, HTS wireaccording to this invention is constructed from the HTS insert (lessmetallic layer 18 b and stabilizer 20 b) as a starting point in theprocess.

In FIG. 2, a roll-to-roll manufacturing process 30 for producing asuperconducting wire, such as HTS wire 10, FIG. 1, using a RABiTSsubstrate for the template and MOD process for the YBCO layer is shown.The process includes substrate rolling and texture annealing at processstep 32 to produce a substrate such as substrate 16, FIG. 1, bufferlayer deposition and sputter buffer deposition of buffer layers areshown in steps 34 and 36, respectively, which produce buffer layers,such as buffer layers 14 of FIG. 1. At steps 38, 40 and 42 the HTS layer(e.g. HTS layer 12, FIG. 1) is deposited by coating the bufferedsubstrate with a solution based (RE)BCO precursor, the precursor isdecomposed, and the (RE)BCO layer is grown. Next, at step 44, Agprotective layers (e.g. layers 18 a/18 b, FIG. 1) are deposited on theHTS layer and the substrate and at step 46 there is an oxygenation heattreatment performed. An optional step in the process is an ionirradiation step 48 which may be used to produce a uniform distributionof pinning microstructures in the HTS layer to improve electricalperformance, in particular in applied magnetic fields. This process stepis more fully described in published patent application, US2017/0062098, incorporated herein by reference. At step 50 in theprocess, stabilizer layers, such as stabilizer layers 20 a/20 b of FIG.1, are deposited, followed by slitting and the application oflaminations at steps 52 and 54, respectively.

It is understood that individual process steps depicted in FIG. 2 can bereplaced when other processes are used for the template, YBCOdeposition, or stabilization.

Using the above described basic HTS wire manufacturing process,additional/different processing steps may be incorporated according tothis invention to produce a HTS wire with increased engineering currentdensity as well as an HTS wire with improved electrical performance inAC applications. The additional processing steps and the HTS wirearchitecture are described with regards to FIGS. 3-7 below.

In FIG. 3, a continuous reel to reel process 60 according to anembodiment of this invention is depicted to include reels 62 and 64carrying HTS insert wire 10 a and 10 b, respectively, which may becomparable to the HTS insert wire described above with regard to FIG. 1(excluding metallic layer 18 b and stabilizer 20 b). There is anadditional reel 68 which carries stabilizer material 70. In oneembodiment, the stabilizer material 70 may include any suitable metalcontaining material and may have a thickness greater than 10 μm. Inanother embodiment the stabilizer layer may have a thickness of 1 to 2μm. In one embodiment the stabilizer layer is copper. In otherembodiments, stabilizer layer 70 comprises a metal selected from thegroup of aluminum, copper, silver, nickel, iron, stainless steel,aluminum alloy, copper alloy, silver alloy, nickel alloy, and ironalloy. It should be noted that while process 60 is shown to be acontinuous process, the process could alternatively be carried out usingtwo or more individual steps.

HTS insert wire 10 a is paid off reel 62 so that its cap layer 72 a isfacing the top surface of stabilizer material 70. HTS insert wire 10 bis paid off reel 64 so that its cap layer 72 b is facing the bottomsurface of stabilizer material 70. The surfaces opposite of the caplayers 72 a and 72 b are substrates layers 74 a and 74 b of HTS insertwires 10 a and 10 b, respectively. The substrate layers 74 a/74 b mayalso include one or more buffer layers. The HTS insert wires 10 a and 10b are positioned on either side of stabilizer 70 and the three materialsare fed through a joining machine 76 which joins the two HTS insertwires 10 a/10 b to opposite surfaces of the stabilizer 70 via thinlayers of a Sn based solder material to produce a double sided HTS wirestructure 80. In another embodiment a thin epoxy, which may be dopedwith material to make it electrically conductive, thermally conductive,or electrically and thermally conductive, is used to bond the HTSinserts 10 a/10 b to opposite surfaces of the stabilizer 70.

The double sided HTS wire structure 80 is introduced to exfoliationdevice 82 causing the substrate layers 74 a and 74 b, including bufferlayers, to be released or exfoliated from each wire 10 a and 10 bexposing HTS layers 75 a and 75 b. The exfoliation process relies on thefact that when the two HTS insert strips 10 a and 10 b are bonded to thestabilizer 70 the weakest interface in the composite strip 80 is betweenthe HTS layer and the oxide buffer layer in the HTS insert strips 10 aand 10 b. This interface has a very low peel or cleavage stress of <1MPa. When the composite strip 80 is fed into the exfoliation device 82the exfoliated inserts 74 a and 74 b are separated from the HTS layers75 a and 75 b on each side of stabilizer 90 by peeling at an angle ofbetween 5 to 85 degrees relative to the surface of stabilizer 90. In analternate embodiment, the exfoliation can be assisted by introduction ofadditional stress between inserts 74 a and 74 b as they are separatedfrom the HTS layers 75 a and 75 b on each side of stabilizer 90 byheating composite strip 80. In another embodiment, the exfoliation maybe assisted by cooling composite strip 80. An exfoliation process wasdescribed in a presentation provided by SuNAM Co., LTD. of Koreaentitled “Recent Progress on SuNAM's Coated Conductor Development;Performance, Price & Utilizing ways, on Sep. 13, 2016, at CoatedConductors For Applications 2016 (CCA2016) conference in Aspen Colo.,USA.

The exfoliated substrates 74 a and 74 b are collected on reels 84 and 86as part of the continuous process 60 leaving composite wire structure90. Composite wire structure 90 includes cap layers 72 a and 72 baffixed to the stabilizer 70 and HTS layers 75 a and 75 exposed andfacing outwardly from the stabilizer layer 70. It should be noted thatthe exfoliated buffered substrates 74 a and 74 b may be reused astemplates to grow new HTS layers thereon and the HTS wires with thepreviously used and exfoliated substrates may be fed through thecontinuous process 60 to be once again exfoliated so that HTS wiresaccording to this invention may be produced. In one embodiment the topbiaxially textured oxide buffer layer 14 may be redeposited on the metalsubstrate 16 before it is used as a template to grow a new HTS layer. Inone embodiment the top buffer layer 14 is CeO₂.

Cap layers are deposited on the outside surfaces of the HTS layers 75 aand 75 b of the composite wire structure 90. The cap layers may eachcomprise silver or a silver alloy or a silver layer and copper layer. Inthe case of a layer of silver in combination with a layer of copper, twodeposition steps would be used. In one embodiment the silver layer maybe deposited by a vacuum deposition and the copper layer may bedeposited by an electrical chemical deposition process. An example of asilver layer and a copper layer is shown in prior art FIG. 1, as silverlayer 18 a combined with copper layer 20 a.

An optional step in the process is an ion irradiation step 48, FIG. 2,which may be used to produce a uniform distribution of pinningmicrostructures in the HTS layer to improve electrical performance, inparticular in applied magnetic fields. In one embodiment the ionirradiation step 48 may be introduced before the deposition of thesilver or silver alloy layer 170. In an alternate embodiment the ionirradiation step 48 may be introduced after the deposition of the silveror silver alloy layer 170.

Composite wire structure 93 with cap layers is fed to wire slitter 94,which slits wire structure 93 using a laser slitter, for example, into aplurality of individual narrower HTS wires 95 that are fed intolamination device 99. Lamination device 99 disposes laminations 96 a and96 b, fed from reels 97 and 98, respectively, on the upper and lowersurfaces of the slit HTS wires 95 to form a plurality of compositedouble HTS layer wires 100, according to an embodiment of the invention.

In one embodiment, lamination device 99 is a solder bath which providesa layer a solder to adhere the laminations to composite wire structure95. It should be noted that lamination layers may each comprise a metalselected from the group of aluminum, copper, silver, nickel, iron,stainless steel, aluminum alloy, copper alloy, silver alloy, nickelalloy, and iron alloy. Also, the lamination layers may have a width thatis greater than the HTS layers by between 0.01 and 2 mm.

In an alternative embodiment, lamination device 99 adheres laminationlayers 96 a/96 b to their respective cap layer via an epoxy, which maybe doped with material to make the epoxy electrically conductive,thermally conductive, or electrically and thermally conductive.

A schematic of the transverse cross-section of double HTS layer wire 100as shown in FIG. 4 includes a first surface of HTS layer 75 a capped bysilver/copper cap layer 72 a adhered to the upper surface of stabilizer70 by solder or epoxy layer 102 a. Also shown is a first surface of HTSlayer 75 b capped by silver/copper cap layer 72 b adhered to the lowersurface of stabilizer 70 by solder or epoxy layer 102 b. A secondsurface, opposite the first surface, of HTS layer 75 a capped by caplayer 104 a adhered to lamination 96 a by solder or epoxy 106 a. Asecond surface, opposite the first surface of HTS layer 75 b capped bycap layer 104 b adhered to lamination 96 b by solder or epoxy 106 b.During the lamination process by lamination device 99, FIG. 3, solder orepoxy fillets 108 a and 108 b are disposed along the length and edges ofeach of the plurality of wires 100 mechanically and electricallyconnecting the laminations 96 a and 96 b.

It should be noted that lamination device 99 may be configured to applyepoxy to adhere the laminations to the cap layers of the HTS wiresinstead of using solder. Moreover, in that case the fillets 108 a/108Balong the length and edges of the HTS wires are also formed of epoxy.The epoxy may be doped with material to make the epoxy electricallyconductive, thermally conductive, or electrically and thermallyconductive Substrate.

As is evident from FIG. 4, the substrate/buffer layers 74 a and 74 b arenot present on double HTS layer wire 100 due to the exfoliation processas shown on FIG. 3. As a result, the I_(c) of the double layer HTS wire100 constructed with the same lamina dimensions and same HTS insertwidth as a non-exfoliated wire 70 is doubled. The thickness of thedouble HTS layer wire 100 is reduced by the difference of thethicknesses of the substrate and buffer layer(s) for each HTS layer 74 aand 74 b plus the thickness of two lamina layers and the thickness ofthe stabilizer layer 70. This, therefore, produces an increase in theengineering current density, J_(e), of the double HTS layer 100 relativeto such a standard single HTS layer non-exfoliated wire Also ofsignificant note, by eliminating the ferromagnetic substrates from thefinal wire product, electrical performance issues associate with wiresutilizing ferromagnetic magnetic substrates are eliminated.

A standard HTS wire, comprised of a 10 mm wide HTS insert containing a1.2 μm thick HTS layer, a 75 μm thick substrate, a 150 nm thick bufferlayer, and lamina with dimensions of 12×0.05 mm, has a minimum criticalcurrent (I_(c)) of about 350 A at 77K, self-field. This results in aminimum J_(e) of about 155 A/mm². The new double layer wire 100, FIG. 4,produced from the same starting HTS insert and lamina along with a 25 nmthick stabilizer strip can have a minimum I_(c) of about 700 A at 77K,self-field. This results in an increase in the minimum J_(e) to about400 A/mm². In FIG. 5, there is shown a continuous reel to reel process150 according to an another embodiment of this invention which includesa single reel 152 carrying HTS insert wire 154, which may be comparableto the HTS insert wire described above with regard to FIG. 1. It shouldbe noted that while process 150 is shown to be a continuous process, theprocess could alternatively be carried out using two or more individualsteps.

There is an additional reel 156 which carries stabilizer material 158.In one embodiment, the stabilizer material 158 may include any suitablemetal containing material and may have a thickness greater than 25 μm.In another embodiment the stabilizer may have a thickness of 10 to 25μm. In one embodiment the stabilizer is copper. In other embodiments,stabilizer layer 158 comprises a metal selected from the group ofaluminum, copper, silver, nickel, iron, stainless steel, aluminum alloy,copper alloy, silver alloy, nickel alloy, and iron alloy.

HTS insert wire 154 is paid off reel 152 so that its cap layer 160 isfacing the top surface of stabilizer material 158. The surface oppositeof the cap layer 160 is substrate 162 of HTS insert wire 154. Thesubstrate 162 may also include one or more buffer layers. The HTS insertwire 154 on one side of stabilizer 158 4 are fed through a joiningmachine 164 which joins the HTS insert 154 to the stabilizer 158 via athin layer of a Sn based solder material to produce a single sided HTSwire structure 166.

In another embodiment a thin epoxy, which may be doped with material tomake it electrically conductive, thermally conductive, or electricallyand thermally conductive, is used to bond the HTS insert 154 to thestabilizer 158 to produce a single sided HTS wire structure 166.

The single sided HTS wire structure 166 is introduced to exfoliationdevice 168 causing the substrate layer 162, including buffer layers, tobe released or exfoliated from the HTS wire 152, exposing HTS layer 170.The exfoliated substrate 162 is collected on reel 172 as part of thecontinuous process 150 leaving composite wire structure 174. Compositewire structure 174 includes cap layer 160 affixed to the stabilizer 158and HTS layer 170 exposed and facing outwardly from the stabilizer layer158. It should be noted that the exfoliated buffered substrate 162 maybe reused as templates to grow new HTS layers thereon and HTS wires withthe previously used and exfoliated substrate may be fed through thecontinuous process 150 to be once again exfoliated so that HTS wiresaccording to this invention may be produced. In one embodiment the topbiaxially textured oxide buffer layer 14 may be redeposited on the metalsubstrate 16 before it is used as a template to grow a new HTS layer. Inone embodiment the top buffer layer 14 is CeO₂.

Composite wire structure 174 is fed into a metallic bath 176 to producea cap layer on top of HTS layer 170. The cap layer may each comprisesilver or a silver alloy or a silver layer and copper layer. In the caseof a layer of silver in combination with a layer of copper, two separatebaths would be used. An example of a silver layer and a copper layer isshown in prior art FIG. 1, as silver layer 18 a combined with copperlayer 20 a.

An optional step in the process is an ion irradiation step 48, FIG. 2,which may be used to produce a uniform distribution of pinningmicrostructures in the HTS layer to improve electrical performance, inparticular in applied magnetic fields. In one embodiment the ionirradiation step 48 may be introduced before the deposition of thesilver or silver alloy layer 170. In an alternate embodiment the ionirradiation step 48 may be introduced after the deposition of the silveror silver alloy layer 170.

Composite wire structure 178 with a cap layer is fed to wire slitter180, which slits wire structure 178 using a laser slitter, for example,into a plurality of individual narrower HTS wires 182 that are fed intolamination device 184. Lamination device 184 disposes a laminationlayers 186 and 188 fed from reels 187 and 189, respectively, on theupper and lower surfaces of the slit HTS wires 182 to form a pluralityof composite single sided HTS layer wires 190.

In one embodiment, lamination device 184 is a solder bath which providesa layer a solder to adhere the laminations to composite wire structure182. It should be noted that lamination layers may each comprise a metalselected from the group of aluminum, copper, silver, nickel, iron,stainless steel, aluminum alloy, copper alloy, silver alloy, nickelalloy, and iron alloy. Also, the lamination layers may have a width thatis greater than the HTS layers by between 0.01 and 2 mm.

In an alternative embodiment, lamination device 184 adheres laminationlayers 186/188 to their respective cap layer via an epoxy, which may bedoped with material to make the epoxy electrically conductive, thermallyconductive, or electrically and thermally conductive.

A transverse cross-section schematic of single sided HTS layer wire 190is shown in FIG. 6 to include a first silver/copper cap layer 160 of HTSlayer 170 adhered to the upper surface of stabilizer 158 by solder orepoxy layer 192. Also shown is a second silver/copper cap layer 194 onHTS layer 170. Cap layer 194 is adhered to lamination 186 by solder orepoxy layer 198. On a second surface, opposite the first surface ofstabilizer 158, lamination 188 is affixed thereto by solder or epoxylayer 200. During the lamination process by lamination device 184, FIG.5, solder or epoxy fillets 202 and 204 are disposed along the length andedges of each of the plurality of wires 190 mechanically andelectrically connecting the laminations 186 and 188.

As is evident from FIG. 4, the substrate/buffer layers 162 is notpresent on single sided HTS layer wire 190 due to the exfoliationprocess as shown on FIG. 5. As a result, the thickness of the singlesided HTS layer wire 190 is reduced by the difference between thesubstrate and buffer layer(s) thickness and the stabilizer layerthickness For a substrate and buffer layer thickness of about 75 μm anda stabilizer layer thickness of about 25 μm this amounts to a thicknessreduction of 50 μm. This, therefore, produces an increase in theengineering current density, J_(e), of the single sided HTS layer 190relative to such a single sided layer structure using non-exfoliatedwire using the same lamina dimensions up to as much as [[non-exfoliatedHTS wire thickness]/[non-exfoliated HTS wire thickness−50 μm]]×100%.Also, as described above, by eliminating the substrate in the final wireproduct, in wires normally utilizing magnetic substrates electricalperformance issues associated with magnetic substrates are overcome.

A standard HTS wire, comprised of a 4 mm wide HTS insert containing a1.2 thick HTS layer, a 75 μm thick substrate and a 150 nm buffer layer,and lamina with dimensions of 4.4×0.15 mm, can have a minimum criticalcurrent (I_(c)) of 150 A at 77K, self-field. This results in a minimumJ_(e) of 85 A/mm². The new single layer 190, FIG. 6, produced from thesame starting HTS insert and lamina along with a 25 nm thick stabilizerstrip can have an I₂ of 150 A. This results in a minimum J_(e) of about100 A/mm².

While preferred embodiments of the present invention have been shown anddescribed herein, various modifications may be made thereto withoutdeparting from the inventive idea of the present invention. Accordingly,it is to be understood the present invention has been described by wayof illustration and not limitation. Other embodiments are within thescope of the following claims.

What is claimed is:
 1. A laminated superconductor wire assembly,comprising: a first high temperature superconductor layer having a firstsurface and a second surface opposite the first surface; a firstelectrically conductive cap layer overlaying and in direct physicalcontact with the first surface of the first high temperaturesuperconductor layer; a second electrically conductive cap layeroverlaying and in direct physical contact with the second surface of thefirst high temperature superconductor layer; a first lamination layeroverlaying and affixed to the first electrically conductive cap layer; astabilizer layer, having a first surface and a second surface oppositethe first surface, the first surface of the stabilizer layer overlayingand affixed to the second electrically conductive cap layer; a secondhigh temperature superconductor layer having a first surface and asecond surface opposite the first surface; a third electricallyconductive cap layer overlaying and in direct physical contact with thefirst surface of the second high temperature superconductor layer; afourth electrically conductive cap layer overlaying and in directphysical contact with the second surface of the second high temperaturesuperconductor layer; a second lamination layer overlaying and affixedto the fourth electrically conductive cap layer; wherein the secondsurface of the stabilizer layer is overlaying and affixed to the thirdelectrically conductive cap layer; and wherein there is included a firstfillet disposed along a first edge of the laminated superconductor wireassembly and connected to the first lamination layer and the secondlamination layer and a second fillet disposed along a second edge of thelaminated superconductor wire assembly and connected to the firstlamination layer and the second lamination layer.
 2. The wire of claim1, wherein the first and second high temperature superconductor layerseach comprise a rare earth-alkaline earth-copper oxide.
 3. The wire ofclaim 1, wherein the first, second, third and fourth electricallyconductive cap layers each comprise silver or a silver alloy or a silverlayer and copper layer.
 4. The wire of claim 1, wherein the first andsecond lamination layers each comprise a metal selected from the groupof aluminum, copper, silver, nickel, iron, stainless steel, aluminumalloy, copper alloy, silver alloy, nickel alloy, and iron alloy.
 5. Thewire of claim 3, wherein the first and second lamination layers have awidth that is greater than the width of the first and second hightemperature superconductor layers.
 6. The wire of claim 5, wherein thewidth of the first and second lamination layers are between 0.01 and 2mm greater than the width of the first and second high temperaturesuperconductor layers.
 7. The wire of claim 1, wherein the stabilizerlayer comprises a metal selected from the group of aluminum, copper,silver, nickel, iron, stainless steel, aluminum alloy, copper alloy,silver alloy, nickel alloy, and iron alloy.
 8. The wire of claim 1,wherein the second electrically conductive cap layer is affixed to thefirst surface of the stabilizer layer via an epoxy or a solder, thefourth electrically conductive cap layer is affixed to the secondsurface of the stabilizer layer via an epoxy or a solder, the firstlamination is affixed to the first electrically conductive cap layer viaan epoxy or a solder, and the second lamination is affixed to the fourthelectrically conductive cap layer via an epoxy or a solder; and whereinthe first and second fillets are formed of an epoxy or a solder.
 9. Thewire of claim 8, wherein the epoxy is doped with material to make theepoxy electrically conductive, thermally conductive, or electrically andthermally conductive.
 10. A method of making a laminated superconductorwire, the method comprising: providing a first superconductor inserthaving a first high temperature superconductor layer with a firstsurface overlaying and in direct physical contact with a first biaxiallytextured substrate and a first electrically conductive cap layeroverlaying and in direct physical contact with a second surface of thefirst superconductor layer; providing a second superconductor inserthaving a second high temperature superconductor layer with a firstsurface overlaying and in direct physical contact with a first surfaceof a second biaxially textured substrate and a second electricallyconductive cap layer overlaying and in direct physical contact with asecond surface of the second superconductor layer; affixing the firstelectrically conductive cap layer of the first superconductor insert toa first surface of a stabilizer layer; and affixing the secondelectrically conductive cap layer of the second superconductor insert toa second surface of a stabilizer layer opposite the first surface of thestabilizer layer; removing the first biaxially textured substrate fromthe first superconductor layer to expose the first surface of the firstsuperconductor layer; and removing the second biaxially texturedsubstrate from the second superconductor layer to expose the firstsurface of the second superconductor layer; affixing a thirdelectrically conductive cap layer to the first surface of the firstsuperconductor layer; and affixing a fourth electrically conductive caplayer to the first surface of the second superconductor layer; andaffixing a first lamination layer to the third electrically conductivecap layer; and affixing a second lamination layer to the fourthelectrically conductive cap layer; wherein the step of affixing thefirst and second lamination layers includes disposing a first filletalong a first edge of the laminated superconductor wire assembly andconnected to the first lamination layer and the second lamination layerand disposing a second fillet along a second edge of the laminatedsuperconductor wire assembly and connected to the first lamination layerand the second lamination layer.
 11. The method of claim 10, wherein thefirst and second high temperature superconductor layers each comprise arare earth-alkaline earth-copper oxide.
 12. The method of claim 10,wherein the first and second biaxially textured substrates each compriseone of a hastelloy or a nickel alloy.
 13. The method of claim 10,wherein the first and second biaxially textured substrates each furthercomprise at least one buffer layer.
 14. The method of claim 10, whereinthe first, second, third and fourth electrically conductive cap layerseach comprise silver or a silver alloy or a layer of silver and a layerof copper.
 15. The method of claim 10, wherein the first and secondlamination layers each comprise a metal selected from the group ofaluminum, copper, silver, nickel, iron, stainless steel, aluminum alloy,copper alloy, silver alloy, nickel alloy, and iron alloy.
 16. The methodof claim 10, wherein the first and second lamination layers have a widththat is greater than the width of the first and second high temperaturesuperconductor layers.
 17. The method of claim 16, wherein the width ofthe first and second lamination layers are between 0.01 and 2 mm greaterthan the width of the first and second high temperature superconductorlayers.
 18. The method of claim 10, wherein the stabilizer layercomprises a metal selected from the group of aluminum, copper, silver,nickel, iron, stainless steel, aluminum alloy, copper alloy, silveralloy, nickel alloy, and iron alloy.
 19. The method of claim 10, whereinthe second electrically conductive cap layer is affixed to the firstsurface of the stabilizer layer via an epoxy or a solder, the fourthelectrically conductive cap layer is affixed to the second surface ofthe stabilizer layer via an epoxy or a solder, the first lamination isaffixed to the first electrically conductive cap layer via an epoxy orsolder, and the second lamination is affixed to the second electricallyconductive cap layer via an epoxy or solder; and wherein the first andsecond fillets are formed of an epoxy or a solder.
 20. The method ofclaim 10, further including reusing the first and second biaxiallytextured substrates removed from the first and second superconductorlayers to produce two superconductor inserts each having a hightemperature superconductor layer with a surface overlaying and in directcontact with one of the removed first and second biaxially texturedsubstrates.